My chickens wont lay in the nest where I found the black snake..

they are using just one nest out of 9.. its getting crowded since i have 12 laying hens.. and some of them cant wait and the eggs are on the ground..
ive changed the hay.. ive cleaned the nest..but the memory lingers on for my girls. what can I do?

Try placing golfballs or fake/wooden eggs in the other nest boxes, about 2 eggs/balls in 2-4 nests should help them feel more safe about laying in them.

How long have they been doing this? If it has only been a few days, then I think they will forget or calm down in time, a couple of weeks maybe. Just make sure to keep the snakes out of the coop, if they see anymore snakes they'll most likely start doing it again.